ABSTRACTThe mechanical properties of sputtered Ni-Al2O3 granular thin films were investigated by low load microharaness testing. It was found that the microhardness of these films displayed a percolation threshold at a nickel volume fraction of about 0.6, below which the hardness is greatly enhanced. This behavior is qualitatively similar to the electrical and magnetic properties of these types of films. A percolation threshold in hardness can be understood as due to a change in the mechanism for plastic deformation.
The influence of interfaces on the morphology of flat spherulites of isotactic polystyrene (iPS) grown in thin films on liquid substrates was investigated. Amorphous iPS thin films spin-cast from a solution were annealed for cold crystallization on glycerol and silicone oil (nonsolvents for iPS). The number density of grown spherulites was revealed to be higher on the glycerol substrate than on the silicone oil substrate. This implies that the primary nucleation rate of crystallization is greater at the iPS/glycerol interface than at the iPS/silicone oil interface. The results may be consistent with the previous findings that concern the molecular interaction between atactic polystyrene and nonsolvents at the interface. In some cases, holes were formed in the thin films during the cold crystallization due to dewetting, which also significantly affect the spherulite morphology via, for example, transcrystallization.
ABSTRACTWafer curvature measurements of a trilayer (SiO2 / AlSiCu / Si) structure are compared to that predicted by a weighted sum of individual measurements of SiO2 and AlSiCu films on Si, and significant differences are found to exist for temperatures above 200°C. A straightforward analysis of the stresses in each layer has been modeled using an extension of a model by Feng et al. which assumes uniform plastic deformation throughout the Al. The modeling results suggest a straightforeward method for determining stresses in deformable thin films that are confined by elastic overlayers. A comparison of the stress-temperature behavior for unpassivated and passivated AlSiCu films reveals that the confined films exhibit less plastic deformation and both higher tension and compression during thermal cycling.
AbstractIn this paper, we explore the use of nanoindentation techniques as a method of measuring equivalent stress-strain curves of the PECVD SiOx thin films. Three indenter tips with different geometries were adopted in our experiments, enabling us to probe different regimes of plastic deformation in the PECVD SiOx thin films. A shear transformation zone (STZ) based amorphous plasticity theory is applied to depict the underlying plastic deformation mechanism.
Based on nanoindentation techniques, the evaluation of hardness of two nanostructured thin films, AlN and Ti-Al-N, is discussed. In the case of AlN films, the indentation size effect of hardness can be modeled using the concept of geometrically necessary dislocations, whereas in the case of Ti-Al-N films, the measured hardness increases exponentially as the indentation depth
decreases. The results show that, as thin films approach superhard, dislocation-based plastic deformation is gradually replaced by grain-boundary mediated deformation.
ABSTRACTThe hillock growth mechanism at the surface of Pt/TiN electrodes is investigated. TEM and SEM observations confirm that local delamination occurs at the Pt/TiN interface first, and then, plastic deformation of the Pt films under compressive stress forms hollow domes, which result in hillocks. Hillocks always start to grow when the internal stress in the Pt films reaches about −1000 MPa during annealing in N2/O2 ambient. Since the initial internal stress of Pt thin films varies from −500 to 500 MPa, depending on their deposition temperature, the hillock growth temperature strongly depends on the deposition temperature of the Pt films. It is very important, therefore, to control the initial internal stress in Pt films in order to eliminate hillock growth at the surface of Pt/TiN electrodes.
Interfacial Effects on the Spherulitic Morphology of Isotactic Polystyrene Thin Films on Liquid Substrates